As a technology of separating oxygen in the air, there are an adsorption method, a sub-zero method, a technology using a separation membrane, and the like. The sub-zero method is a technology of separating nitrogen and oxygen by cooling air with cryogenic temperature and the oxygen separation using the separation membrane uses a polymeric separation membrane, a high temperature ceramic separation membrane, and the like for oxygen separation using the separation membrane.
The oxygen separation in the air using adsorption is based on a technology of adsorbing and removing nitrogen in the air and producing high-concentration oxygen by using zeolite as an adsorption agent selectively adsorbing a nitrogen component in the air. A process for selectively adsorbing and removing nitrogen and producing high-concentration oxygen requires an adsorption and desorption tower having a large volume since nitrogen occupying the majority of air is adsorbed and removed and is hardly produce the high-purity oxygen due to low selectivity for nitrogen. Generally, an adsorption separation process using a nitrogen absorption agent is suitable to produce oxygen of 95% or less.
To supplement the disadvantage of the nitrogen-selecting adsorption agent, efforts to develop an adsorption agent selectively adsorbing oxygen at high temperature and produce high-concentration oxygen have been attempted recently.
U.S. Pat. No. 6,361,584 discloses a technology of selectively adsorbing oxygen in the air at high temperature using a metal oxide of La1-ySryCuO4-x and produces high-purity oxygen by reducing a pressure and U.S. Pat. No. 6,059,858 discloses a process of adsorbing oxygen at high temperature by using a metal oxide having a A1-xMxBO3-d structure and desorbing the adsorbed oxygen by using gas without oxygen.
Barium oxide has been well known as a material which is converted into barium peroxide by reacting to oxygen and thus suffering from oxidation reaction represented by the following Chemical Formula 1 and during the process, adsorbs oxygen and discharges oxygen by a reduction reaction under the atmosphere in which oxygen is not present. Therefore, due to characteristics of the barium oxide, the barium oxide has been used in a process of producing oxygen in the early part of the 20th century.BaO+½O2→BaO2  [Chemical Formula 1]
However, the barium peroxide does not have thermal stability at high temperature and therefore tends to lose oxygen adsorption ability while the cycle is progressed. In more detail, the barium peroxide which is a considerably thermally instable material may cause a sintering phenomenon between particles at high temperature, and therefore a size of the particle is increased and the oxygen adsorption ability is gradually lost while the process is progressed. Therefore, the oxygen-selective adsorption agent which may keep the adsorption ability only when the sintering phenomenon is prevented may be produced. Further, the barium peroxide has excellent reactivity to easily react to other inorganic materials or metal components and therefore loses bonding characteristics with oxygen. Therefore, a structure in which a barium component (barium oxide) selectively adsorbing oxygen may be stably protected is required.
In order to cope with the above problem, various methods have been attempted. In connection with this, U.S. Pat. Nos. 3,773,680 and 3,903,010 disclose that barium oxide is fixed to dolomite to be able to increase utilization and reactivity of barium. In the above U.S. Patents, in order to produce the oxygen-selective adsorption agent, a method for simply mixing barium oxide with a dolomite solid and forming the mixture in a pellet form at a high pressure has been used.
U.S. Pat. No. 4,092,264 discloses that an oxygen adsorption agent having high utilization and stability of barium by impregnating barium oxide into zirconia may be produced. A method for impregnating the barium oxide disclosed in U.S. Pat. No. 4,092,264 is as follows. First, the barium peroxide is impregnated into the zirconia by removing impurities by firing porous zirconia at high temperature, mixing the zirconia with the barium oxide, and heating the acquired mixture. The above patent discloses that when the barium peroxide is impregnated into the zirconia by the above-mentioned method, thermal stability may be improved, since heat generated from the oxidation reaction with oxygen while the oxygen production process is operated is effectively stored and then the heat is used at the time of the reduction reaction, process efficiency may be increased, and when barium of 20% or less is impregnated into zirconia, the thermal stability may be highest and the utilization of barium may also be increased.
According to the above patents, a method for mixing barium peroxide and a third base material with each other or impregnating barium peroxide into a third base material in a dried condition has been mainly used. However, in the case of using the method for mixing barium peroxide and a third base material with each other, a non-uniform protective film is formed and thus the utilization of the barium oxide is not high and in the case of using the method for impregnating barium peroxide into a third base material, a large quantity of material acting as a base material needs to be used, and therefore a material having high oxygen adsorption ability may not be developed.
According to another method, barium oxide may be collected in a frame of magnesium oxide by mixing the barium oxide with the magnesium oxide using a precursor (water-soluble magnesium salt) of magnesium oxide in an aqueous solution and then inducing evaporation of water to form precipitates and performing high temperature firing process on the precipitates. However, the method forms barium hydroxide by reaction between the barium oxide and moisture during the firing process. By the way, since the barium hydroxide has low stability and high reactivity, the method has a problem in that it is difficult to perform the firing and even after the firing is performed, the adsorption ability of oxygen is degraded.